Approximately 90% of all drugs used to produce a systemic effect are administered via the oral route. Of those administered orally, tablets are preferred for a variety of reasons. For example, tablets are unit dose forms that offer the greatest uniformity of content, in a light and compact package. In addition, tablets are relatively simple and inexpensive to produce, package, and ship. Tablets also offer the greatest ease of swallowing, especially when coated, they easily lend themselves to certain special-release profile products, such as enteric or delayed-release products, and they have the best combined properties of chemical, mechanical, and microbiological stability of all oral dosage forms. For at least these reasons, a wide variety of medications are currently available in tablet form. However, oral dosage forms are not free from abuse, especially certain analgesics that are capable of rapid pain relief with a simultaneous euphoric effect.
Enteric coatings have been used to modify drug release in oral dosage forms. Enteric coatings are designed to remain intact in the stomach, but will dissolve and release the contents of the dosage form in the small intestine. The coatings are generally used to delay the release of drugs that are inactivated by the stomach contents or that may irritate the gastric mucosa, thereby causing nausea or bleeding. The action of enteric coatings results from a difference in composition of the gastric and intestinal environments with respect to pH and the presence of endogenous enzymes. Most enteric coatings are formulated to remain intact in the low pH of the stomach, but readily dissolve when the pH rises to about 4–5. The most effective enteric polymers are poly acids having a pKa of 3–5. See Remington: The Science and Practice of Pharmacy, 19th Ed., Ed. Alfonso R. Gennaro, et al., Philadelphia College of Pharmacy and Science (1995), p. 1653 et seq. However, enteric coatings have not been used to deter abuse and provide a tamper resistant dosage form.
U.S. Pat. No. 5,507,277 to Rubsamen, et al., relates to a method of controlling access to a drug that is administered by an intrapulmonary delivery device having an electronic lock and key mechanism. Access to the drug in the device is limited to the intended user by providing that user with a uniquely coded, machine readable key that matches the code on the device lock. Contacting the lock and key signals a controlling means within the device to permit use of the device. However, Rubsamen does not address the unique problems posed by abuse of oral dosage forms.
Therefore, a need exists for an oral dosage form that delivers medication when taken as directed, but when abused, the normal delivery mechanism is circumvented or interrupted to prevent abuse by an unintended user.